Aragonite is a polymorph of calcium carbonate that typically forms in distinct orthorhombic prismatic crystals or unique 'flos ferri' coralloid clusters. It is frequently found in limestone caves and hot spring deposits, where it precipitates from groundwater. Collectors should look for its characteristic star-shaped twinned crystals and its common yellow or white color palette.
Is this aragonite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch aragonite with a known reference. Aragonite sits at Mohs 3.5-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, resinous on fracture surfaces.
- 4Match the color rangeCompare against the expected color range: white, colorless, yellow, blue, green, brown, gray, yellowish white, reddish white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: columnar, fibrous, pseudo hexagonal.
Often confused with
Aragonite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside aragonite
Minerals reported to co-occur with aragonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaCO₃
- Mohs hardness
- 3.5-4
- Density
- 2.95 g/cm³
- Streak
- White
- Luster
- Vitreous, resinous on fracture surfaces
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Columnar, fibrous, pseudo hexagonal
- Cleavage
- {010}, distinct; {110} and {011}, imperfect
- Fluorescence
- Green under SW and LW UV
- Rarity
- Common
- Uses
- Collector, Ornamental, Scientific research
- Host rock
- Converts to calcite over geologic time
Where rockhounds find aragonite
25 mapped spotsClassic worldwide localities
- Caves at Bisbee, Cochise Co., Arizona, USA
- Lake Arthur, Chavez Co., also near Santa Rosa, Guadalupe Co., New Mexico, USA
- Passaic mine, Sterling Hill, Ogdensburg, Sussex Co., New Jersey, USA
- Molina, Guadalajara Province, Spain
- Racalmuto, Cianciana, and Agrigento, Sicily, Italy
- Dognácska and Špania Dolina (Herrengrund), Slovakia
U.S. states with aragonite
Each link opens a state-specific list of mapped rockhounding spots that produce aragonite.
Field-hunting tip
Where it forms: Converts to calcite over geologic time. If you start seeing gypsum, sulfur, celestine in float, you are in the right ground. Typical habit: columnar, fibrous, pseudo hexagonal. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Missouri, Utah, Indiana. Start trip planning there.
More aragonite photos
Common questions
How do you identify aragonite?+
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Can I find aragonite in the United States?+
What rocks look like aragonite?+
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Find aragonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
